Are more North American species decreasing than increasing?

Population trends for North American species are calculated for 1966-'91 and 1982-'91 using Nonh American Breeding Bird Survey data. Species are grouped into 3 systems of guild classifications representing migration status, breeding habitat and nesting substrate. Trends for these groups are summarized by time period, bioregion and physiographic region. At the continental level, declines approximately equalled increases. There are slightly more declines during the last 10 years. Prairie populations declined more than expected, while western populations increased. Scrub and grassland nesting species declined significantly in several bioregions while woodland species increased. Most guilds did not depart significantly from a ratio of 50:50 increases to decreases or have opposing trends in different bioregions. Guild group changes are usually clustered geographically. Guild and other analyses that search for patterns among population trend estimates offer an excellent means of identifying critical conservation issues.